EOF Analysis of the Model SSS

To characterize the SSS variability we computed the Empirical Orthogonal Functions (EOFs) of the SSS time series. The first three modes account for approximately half (52%) of the total SSS variance. The first EOF, which explains 30% of the variance, represents seasonal oscillations of the freshwater plumes along the shelf. 

The second EOF mode, which accounts for approximately 15% of the variance, represents the impact of the Rio de la Plata discharge over the shelf salinities. There is an approximate 2.5 months lag between the time series of the second EOF and the river discharge. 

The third EOF mode represents the SSS anomalies associated with the exchanges between the continental shelf and the deep ocean. This mode only explains 7% of the total variance, however, if the salinity values over the shelf are excluded, this EOF becomes the leading mode of SSS variability of the deep ocean portion of the southwestern Atlantic, explaining approximately 25% of its total variance. That is, the relatively small percentage of the total variability accounted for this mode only reflects the fact that SSS variations over the shelf are much larger than those over the deep ocean. The spatial structure of the third EOF is characterized by a maximum that extends along the coast of Uruguay and southern Brazil and a minimum that spreads as a tongue from the middle shelf into the deep ocean. The largest amplitudes of this tongue are observed over the shelfbreak, in the latitudinal range extending from approximately 37˚ to 32˚S. 

This tongue follows the contour of the BMC, thus suggesting a relation between the offshore detrainment of the shelf waters and the dynamics of the western boundary currents. The relationship between the detrainments of the waters from the Rio de la Plata and the Brazil/Malvinas Confluence is further explored in the section on the "escape latitude".